1. Field of the Invention
The present invention relates to an ionomer-type luminescent polymer and polymeric electroluminescent devices employing the same, more specifically, to an ionomer-type luminescent polymer whose heat-stability is improved by the formation of ionic cross-linkage, and electroluminescent devices employing the same as a luminescent layer.
2. Background of the Invention
Most of the luminescent materials used for polymeric electroluminescent devices are not linked to ions. The luminescent materials are, depending on the backbone structure, generally classified into conjugated polymer, non-conjugated luminescent polymer, and conjugated/non-conjugated multi-block copolymer with alternating conjugated and non-conjugated parts. Conjugated luminescent polymers having xcfx80-conjugated double bond backbone, includes poly(1,4-phenylenevinylene, PPV) (see: U.S. Pat. No. 5,247,190) and its derivatives, derivatives of poly(para-phenylene) (see: G. Grem et al, Advanced Materials, 4(36), 1992), derivatives of polythiophen(see: U.S. Pat. No. 5,540,999), and derivatives of polyphlorene(see: U.S. Pat. No. 5,876,864). Non-conjugated luminescent polymers have non-luminescent backbone connected to luminescent side chains with fluorescent materials such as anthracene, to give electroluminescence corresponding to a luminescent region attributed by the fluorescent material. On the other hand, luminescent polymers made of conjugated/non-conjugated multi-block have a structure in which the length of the conjugation is made short to create blue-shift of luminescent region.
Most of polymeric electroluminescent devices, however, are proven to be less satisfactory in the senses that they are able a to emit blue light only at more than 10 V, and have short life span. As an alternative, Vera Cimnova et al. has reported water-soluble, ionic luminescent polymers by introducing ionic groups into backbone in the form of electrolytes. However, they still revealed a shortcoming of short life-span, owing to the unstable nature of polymers in the environment of water and high temperature(see: Vera Cimnova at al., Applied Materials, 8, 585, 1996).
Therefore, there are strong reasons for developing and exploring novel luminescent polymers that can emit light at a low voltage, while enjoying long life-span.
The present inventors have made an effort to provide luminescent polymers of long life-span that can emit light at a low voltage, and discovered that ionomer-type luminescent polymers prepared by introducing ionic groups into luminescent polymers can emit light at a low voltage, and have higher stability to water and long life-span.
A primary object of the present invention is, therefore, to provide ionomer-type luminescent polymers.
The other object of the invention is to provide electroluminescent devices employing a luminescent layer of ionomer-type electroluminescent polymer.